How the Chicxulub impactor gave rise to modern rainforests

Date:
April 2, 2021
Source:
Smithsonian Tropical Research Institute
Summary:
The asteroid that took out the dinosaurs left the planet in
darkness.

What did rainforests in South America look like before the impact,
and how did they change as a result?


FULL STORY ========================================================================== About 66 million years ago, a huge asteroid crashed into what is now
the Yucatan, plunging the Earth into darkness. The impact transformed
tropical rainforests, giving rise to the reign of flowers.


========================================================================== Tropical rainforests today are biodiversity hotspots and play an
important role in the world's climate systems. A new study published
today in Science sheds light on the origins of modern rainforests and
may help scientists understand how rainforests will respond to a rapidly changing climate in the future.

The study led by researchers at the Smithsonian Tropical Research
Institute (STRI) shows that the asteroid impact that ended the reign
of dinosaurs 66 million years ago also caused 45% of plants in what is
now Colombia to go extinct, and it made way for the reign of flowering
plants in modern tropical rainforests.

"We wondered how tropical rainforests changed after a drastic ecological perturbation such as the Chicxulub impact, so we looked for tropical plant fossils," said Mo'nica Carvalho, first author and joint postdoctoral
fellow at STRI and at the Universidad del Rosario in Colombia. "Our
team examined over 50,000 fossil pollen records and more than 6,000
leaf fossils from before and after the impact." In Central and South
America, geologists hustle to find fossils exposed by road cuts and mines before heavy rains wash them away and the jungle hides them again. Before
this study, little was known about the effect of this extinction on the evolution of flowering plants that now dominate the American tropics.

Carlos Jaramillo, staff paleontologist at STRI and his team, mostly STRI fellows -- many of them from Colombia -- studied pollen grains from 39
sites that include rock outcrops and cores drilled for oil exploration
in Colombia, to paint a big, regional picture of forests before and
after the impact. Pollen and spores obtained from rocks older than the
impact show that rainforests were equally dominated by ferns and flowering plants. Conifers, such as relatives of the of the Kauri pine and Norfolk
Island pine, sold in supermarkets at Christmas time (Araucariaceae), were common and cast their shadows over dinosaur trails. After the impact,
conifers disappeared almost completely from the New World tropics, and flowering plants took over. Plant diversity did not recover for around
10 million years after the impact.



==========================================================================
Leaf fossils told the team much about the past climate and local
environment.

Carvalho and Fabiany Herrera, postdoctoral research associate at the
Negaunee Institute for Conservation Science and Action at the Chicago
Botanic Garden, led the study of over 6,000 specimens. Working with Scott
Wing at the Smithsonian's National Museum of Natural History and others,
the team found evidence that pre-impact tropical forest trees were spaced
far apart, allowing light to reach the forest floor. Within 10 million
years post-impact, some tropical forests were dense, like those of today,
where leaves of trees and vines cast deep shade on the smaller trees,
bushes and herbaceous plants below.

The sparser canopies of the pre-impact forests, with fewer flowering
plants, would have moved less soil water into the atmosphere than did
those that grew up in the millions of years afterward.

"It was just as rainy back in the Cretaceous, but the forests worked differently." Carvalho said.

The team found no evidence of legume trees before the extinction event,
but afterward there was a great diversity and abundance of legume leaves
and pods.

Today, legumes are a dominant family in tropical rainforests, and through associations with bacteria, take nitrogen from the air and turn it into fertilizer for the soil. The rise of legumes would have dramatically
affected the nitrogen cycle.

Carvalho also worked with Conrad Labandeira at the Smithsonian's National Museum of Natural History to study insect damage on the leaf fossils.

"Insect damage on plants can reveal in the microcosm of a single leaf or
the expanse of a plant community, the base of the trophic structure in
a tropical forest," Labandeira said. "The energy residing in the mass of
plant tissues that is transmitted up the food chain -- ultimately to the
boas, eagles and jaguars -- starts with the insects that skeletonize,
chew, pierce and suck, mine, gall and bore through plant tissues. The
evidence for this consumer food chain begins with all the diverse,
intensive and fascinating ways that insects consume plants." "Before the impact, we see that different types of plants have different damage:
feeding was host-specific," Carvalho said. "After the impact, we find
the same kinds of damage on almost every plant, meaning that feeding
was much more generalistic." How did the after effects of the impact
transform sparse, conifer-rich tropical forests of the dinosaur age into
the rainforests of today -- towering trees dotted with yellow, purple and
pink blossoms, dripping with orchids? Based on evidence from both pollen
and leaves, the team proposes three explanations for the change, all of
which may be correct. One idea is that dinosaurs kept pre- impact forests
open by feeding and moving through the landscape. A second explanation is
that falling ash from the impact enriched soils throughout the tropics,
giving an advantage to the faster-growing flowering plants. The third explanation is that preferential extinction of conifer species created
an opportunity for flowering plants to take over the tropics.

"Our study follows a simple question: How do tropical rainforests evolve?" Carvalho said. "The lesson learned here is that under rapid disturbances
- - geologically speaking -- tropical ecosystems do not just bounce
back; they are replaced, and the process takes a really long time."
The Smithsonian Tropical Research Institute, headquartered in Panama
City, Panama, is a unit of the Smithsonian Institution. The institute
furthers the understanding of tropical biodiversity and its importance
to human welfare, trains students to conduct research in the tropics
and promotes conservation by increasing public awareness of the beauty
and importance of tropical ecosystems.

========================================================================== Story Source: Materials provided by
Smithsonian_Tropical_Research_Institute. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Mo'nica R. Carvalho, Carlos Jaramillo, Felipe de la Parra, Dayenari
Caballero-Rodri'guez, Fabiany Herrera, Scott Wing, Benjamin
L. Turner, Carlos D'Apolito, Millerlandy Romero-Ba'ez, Paula
Narva'ez, Camila Marti'nez, Mauricio Gutierrez, Conrad Labandeira,
German Bayona, Milton Rueda, Manuel Paez-Reyes, Dairon Ca'rdenas,
A'lvaro Duque, James L.

Crowley, Carlos Santos, Daniele Silvestro. Extinction at
the end- Cretaceous and the origin of modern Neotropical
rainforests. Science, 2021; 372 (6537): 63 DOI:
10.1126/science.abf1969 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/04/210402095949.htm

--- up 1 week, 1 day, 8 hours, 39 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)